Fluoroapatite has almost the same crystalline structure as hydroxyapatite, and therefore shows almost the same adsorption characteristics (adsorption ability) to a protein as hydroxyapatite.
Further, fluoroapatite is a substance that is stabler than hydroxyapatite, and therefore has high acid resistance. For these reasons, fluoroapatite has advantages that it has high resistance to acid solutions, and therefore is capable of separating proteins in an acid solution.
Such fluoroapatite is generally synthesized by adding (mixing) ammonium hydrogen fluoride as a fluorine source into (with) a slurry containing hydroxyapatite (JP A-2004-330113 is an example of related art.).
However, the fluoroapatite synthesized by such a method contains ammonia adsorbed thereto as an impurity. Apatites such as fluoroapatite have a high ability to adsorb ammonia, and therefore in a case where a slurry containing synthesized fluoroapatite is spray-dried (granulated) to obtain particles, ammonia remains in the particles (fluoroapatite particles) because it is very difficult to remove ammonia from the particles.
Therefore, an amount of ammonia remaining in the thus produced particles is different from lot to lot, which makes it difficult to obtain particles having uniform characteristics.
Further, ammonia remaining in fluoroapatite (particles) inhibits substitution of hydroxyl groups by fluorine atoms, and therefore there are also problems that a rate of the substitution of hydroxyl groups by fluorine atoms can be increased only to a certain extent and therefore it cannot be expected that acid resistance of fluoroapatite is further improved.